Training Sequence Indication for WLAN

1. A method for generating a data unit for transmission via a multiple input, multiple output (MIMO) communication channel, the method comprising: generating, at a communication device, a plurality of training sequences to be included in a preamble of the data unit; when the data unit is to be transmitted in a single user mode in which the data unit is intended for a single receiver, generating, at the communication device, a first field of the preamble to include an indicator that the data unit is being transmitted in the single user mode, and generating, at the communication device, a second field of the preamble to include bits of an identifier of the single receiver; when the data unit is being transmitted in a multi-user mode in which the data unit is intended for multiple receivers, generating, at the communication device, the first field of the preamble to include an indicator that the data unit is being transmitted in the multi-user mode, and generating, at the communication device, the second field of the preamble to include one or more indications of one or more sets of training signals in the preamble, the one or more sets of training signals corresponding to transmission of the data unit to one or more receivers; generating, at the communication device, the preamble such that the first field of the preamble and the second field of the preamble will be transmitted prior to the plurality of training sequences being transmitted; and generating, at the communication device, the data unit to include the preamble such that, when the data unit is transmitted in the single user mode, the preamble includes i) the indicator that the data unit is being transmitted in the single user mode in the first field, and ii) bits of the identifier of the single receiver in the second field, and when the data unit is transmitted in the multi-user mode, the preamble includes i) the indicator that the data unit is being transmitted in the multi-user mode in the first field, and ii) the one or more indications of one or more sets of training signals in the second field.

2. The method of claim 1 , further comprising: when the data unit is to be transmitted in the single user mode, generating, at the communication device, a third field of the preamble to include modulation and coding scheme information for the data unit; and when the data unit is being transmitted in the multi-user mode, generating, at the communication device, a fourth field of the preamble to include modulation and coding scheme information for the data unit, wherein the fourth field is separate from the third field.

3. The method of claim 1 , further comprising: when the data unit is to be transmitted in the single user mode, generating, at the communication device, a third field of the preamble to include an indication of a number of spatial or space time streams; and when the data unit is being transmitted in the multi-user mode, generating, at the communication device, the third field of the preamble to include an indication of a number of spatial or space time streams corresponding to a first receiver among the multiple receivers.

4. The method of claim 3 , wherein: when the data unit is being transmitted in the multi-user mode, the one or more indications of one or more sets of training signals in the preamble comprise one or more indications of one or more numbers of spatial or space time streams corresponding to one or more second receivers among the multiple receivers.

5. The method of claim 1 , wherein generating the second field of the preamble to include bits of the identifier of the single receiver comprises generating the second field of the preamble to include only a subset of bits of the identifier of the single receiver.

6. The method of claim 1 , wherein generating the second field of the preamble to include bits of the identifier of the single receiver comprises generating the second field of the preamble to include bits of an association identifier (AID) of the single receiver.

7. An apparatus, comprising: a physical layer (PHY) processing device having one or more integrated circuits configured to: generate a plurality of training sequences to be included in a preamble of a data unit to be transmitted via a multiple input, multiple output (MIMO) communication channel, when the data unit is to be transmitted in a single user mode in which the data unit is intended for a single receiver, generate a first field of the preamble to include an indicator that the data unit is being transmitted in the single user mode, and generate a second field of the preamble to include bits of an identifier of the single receiver, when the data unit is being transmitted in a multi-user mode in which the data unit is intended for multiple receivers, generate the first field of the preamble to include an indicator that the data unit is being transmitted in the multi-user mode, and generate the second field of the preamble to include one or more indications of one or more sets of training signals in the preamble, the one or more sets of training signals corresponding to transmission of the data unit to one or more receivers; wherein the one or more integrated circuits are further configured to: generate the preamble such that the first field of the preamble and the second field of the preamble will be transmitted prior to the plurality of training sequences being transmitted, and generate the data unit to include the preamble such that, when the data unit is transmitted in the single user mode, the preamble includes i) the indicator that the data unit is being transmitted in the single user mode in the first field, and ii) bits of the identifier of the single receiver in the second field, and when the data unit is transmitted in the multi-user mode, the preamble includes i) the indicator that the data unit is being transmitted in the multi-user mode in the first field, and ii) the one or more indications of one or more sets of training signals in the second field.

8. The apparatus of claim 7 , wherein the one or more integrated circuits are further configured to: when the data unit is to be transmitted in the single user mode, generate a third field of the preamble to include modulation and coding scheme information for the data unit, and when the data unit is being transmitted in the multi-user mode, generate a fourth field of the preamble to include modulation and coding scheme information for the data unit, wherein the fourth field is separate from the third field.

9. The apparatus of claim 7 , wherein the one or more integrated circuits are further configured to: when the data unit is to be transmitted in the single user mode, generate a third field of the preamble to include an indication of a number of spatial or space time streams, and when the data unit is being transmitted in the multi-user mode, generate the third field of the preamble to include an indication of a number of spatial or space time streams corresponding to a first receiver among the multiple receivers.

10. The apparatus of claim 9 , wherein: when the data unit is being transmitted in the multi-user mode, the one or more indications of one or more sets of training signals in the preamble comprise one or more indications of one or more numbers of spatial or space time streams corresponding to one or more second receivers among the multiple receivers.

11. The apparatus of claim 7 , wherein the one or more integrated circuits are configured to generate the second field of the preamble to include only a subset of bits of the identifier of the single receiver when the data unit is to be transmitted in the single user mode.

12. The apparatus of claim 7 , wherein the one or more integrated circuits are configured to generate the second field of the preamble to include bits of an association identifier (AID) of the single receiver when the data unit is to be transmitted in the single user mode.

13. A method for processing a data unit received via a multiple input, multiple output (MIMO) communication channel, the method comprising: processing, at a communication device, a first field of a preamble of a data unit to determine whether the data unit was transmitted in i) a single user mode in which the data unit is intended for a single receiver or ii) a multi-user mode in which the data unit is intended for multiple receivers; when it is determined that the data unit was transmitted in the single user mode, processing, at the communication device, a second field of the preamble that includes bits of an identifier of the single intended receiver to determine whether the data unit is intended for the communication device; and when it is determined that the data unit was transmitted in the multi-user mode, processing, at the communication device, the first field of the preamble to determine whether the data unit is intended for the communication device, and processing, at the communication device, the second field of the preamble to determine a set of training signals in the preamble corresponding to transmission of the data unit to the communication device, wherein the second field of the preamble is received at the communication device prior to receiving the set of training signals.

14. The method of claim 13 , further comprising: when it is determined that the data unit was transmitted in the single user mode, processing, at the communication device, a third field of the preamble to determine modulation and coding scheme information for the data unit; and when it is determined that the data unit was transmitted in the multi-user mode, processing, at the communication device, a fourth field of the preamble to determine modulation and coding scheme information for the data unit, wherein the fourth field is separate from the third field.

15. The method of claim 13 , further comprising: when it is determined that the data unit was transmitted in the single user mode, processing, at the communication device, a third field of the preamble to determine a number of spatial or space time streams for the data unit.

16. The method of claim 13 , wherein: when it is determined that the data unit was transmitted in the single user mode, processing the second field of the preamble to determine whether the data unit is intended for the communication device includes interpreting the second field of the preamble as including only a subset of bits of the identifier of the single intended receiver.

17. The method of claim 13 , wherein: when it is determined that the data unit was transmitted in the single user mode, processing the second field of the preamble to determine whether the data unit is intended for the communication device includes interpreting the second field of the preamble as including bits of an association identifier (AID) of the single intended receiver.

18. An apparatus, comprising a physical layer (PHY) processing device having one or more integrated circuits configured to: process a first field of a preamble of a data unit to determine whether the data unit was transmitted in i) a single user mode in which the data unit is intended for a single receiver or ii) a multi-user mode in which the data unit is intended for multiple receivers, when it is determined that the data unit was transmitted in the single user mode, process a second field of the preamble that includes bits of an identifier of the single intended receiver to determine whether the data unit is intended for the communication device, and when it is determined that the data unit was transmitted in the multi-user mode, process the first field of the preamble to determine whether the data unit is intended for the communication device, and process the second field of the preamble to determine a set of training signals in the preamble corresponding to transmission of the data unit to the communication device, wherein the second field precedes the set of training signals in the preamble.

19. The apparatus of claim 18 , wherein the one or more integrated circuits are further configured to: when it is determined that the data unit was transmitted in the single user mode, process a third field of the preamble to determine modulation and coding scheme information for the data unit, and when it is determined that the data unit was transmitted in the multi-user mode, process a fourth field of the preamble to determine modulation and coding scheme information for the data unit, wherein the fourth field is separate from the third field.

20. The apparatus of claim 18 , wherein the one or more integrated circuits are further configured to: when it is determined that the data unit was transmitted in the single user mode, process a third field of the preamble to determine a number of spatial or space time streams for the data unit.

21. The apparatus of claim 18 , wherein the one or more integrated circuits are further configured to: when it is determined that the data unit was transmitted in the single user mode, interpret the second field of the preamble as including only a subset of bits of the identifier of the single intended receiver.

22. The apparatus of claim 18 , wherein the one or more integrated circuits are further configured to: when it is determined that the data unit was transmitted in the single user mode, interpret the second field of the preamble as including bits of an association identifier (AID) of the single intended receiver.